Trans lines replaced - Now CEL on..UUGGGHHH!!!

Dropped my truck off this morning at a local repair shop with leaky transmission lines. Shop had it "fixed" by 12:00pm so I stopped by to pay for it ($158) and get my key back. Receipt shows they replaced 3 trans lines. Wife brings me to the shop tonight to pick up the truck and the CEL is now on. So, I shut off and dropped the key back into the key drop. I'll be calling them back in the morning.

Any idea what they could have done in the process of changing trans lines to cause a CEL??

without knowing the codes that the cel is on for it really isnt easy... and it could have just been something that was on its way out as well. Year make and model would help in the future too thanks.

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Sorry about that, I was venting a little frustration at the time. Its a 2007 Classic LT with the 4.8L V8. I would of fixed it myself if it wasnt 30 degrees out. I ashould have more information this afternoon. Thanks for the reply!

Turns out the mechanic "bumped" the MAF sensor. He had it fixed this morning before I even got a chance to call. Got the truck home tonight after dark so I havent had a a chance to inspect his work. Just glad to have it home!